The present invention comprises a new and distinct cultivar of mushroom of the Species Agaricus bisporus (Lange) Imbach (button mushroom) named ‘Broncoh’. The new variety is of the Fungi Kingdom, the Basidomycotina Phylum, and the Agaricaceae Family.
The button mushroom of commerce (Agaricus bisporus) is one of the most commercially cultivated mushrooms worldwide (estimated world production of 2 million metric tons in 2002). It is grown on a substrate called compost. This substrate consists of wheat straw, horse manure, chicken manure, gypsum and water and is fermented in tunnels in three phases. The substrate is inoculated with spawn. Spawn consists of grain (usually wheat) that is boiled in water, sterilized and inoculated with a pure culture of vegetative mycelium. After the grain is fully colonized the spawn is stored at 4 to 8° C. in plastic bags of 15 kg before being used to inoculate substrate. The spawn production is done in especially equipped plants on a large scale. Spawn is mixed with phase II compost and colonized in tunnels at 26° C. The full grown compost (spawn run compost) is transported to growing houses and filled in beds (usually two rows of shelfs, 4 to 6 high, and 90 to 100 kg of compost/m2). The growing houses are equipped with climate control systems. The fully colonized compost is covered with a casing soil layer of approximately 5 cm thickness. The casing soil consists of peat and lime. After the colonization of the casing soil (10 days at 26° C., with hardly no air movement) the climate in the growing house is changed to initiate fruiting body formation. The air temperature is decreased to 16-18° C. by venting the air (letting in of fresh air from outside the growing house). After 10to 14 days mushrooms are picked either by hand (for the fresh market) or cut and harvested mechanically (for canning). Two types of strains are cultivated world wide, i.e. white and brown strains producing mushrooms with a white or brown cap color, respectively. Within the white strains, three types of varieties are cultivated, whereas within the brown strains, only one variety is used. The brown strains are either picked at an early developmental stage or when fully matured. In the former case, mushroom caps are usually closed. In the latter case, caps are fully open so that the gills, producing the spores, are fully exposed. These types of mushrooms are designated as Portabellos or Portabellas.
The life cycle of A. bisporus has been well studied in the past. The compatibility of strains is controlled by one mating-type factor and different alleles are needed for fertility. Fertile vegetative mycelium consists of a network of cells, each of which has a variable number of two genetically distinct nuclei with opposite mating type (heterokaryon). In the basidia, specialized cells on the lamellae that produce spores, the number of nuclei is reduced to two, one of each mating type. After nuclear fusion, a normal meiosis takes place. Most basidia, however, produce two spores, each containing two non-sister nuclei (n+n). Fruiting tests show that these single spore cultures can produce mushrooms, i.e. that they contain both mating types. Besides this heteroallelism for the mating type, A. bisporus maintain in general the parental heterogeneity. This can be explained by assuming that there is a mechanism that favors the pairing of non-sister nuclei and that there is a low percentage of recombination in meiosis. The former is supported by microscopic observations that show a meiotic spindle orientation resulting in 80% of the spores incorporating non-sister nuclei. Several reports have also shown an unusually low recombination in A. bisporus. Only a small percentage of the basidia produce 3 or 4 spores. Most of these spores are haploid (n) and do not fruit or form only a limited number of fruit bodies. Single spore cultures derived from these types of spores produce a vegetative mycelium that also contain a variable number of (genetically identical) nuclei per cell (homokaryon). This secondary homothallic life cycle is found in all commercial lines and in field isolates from Alberta, coastal California and France. Other characteristics of A. bisporus are, besides the variable number of nuclei in both homo- and heterokaryons, the lack of clamp connections in heterokaryons. The typical life cycle and the lack of differences between homo- and heterokaryons are a serious drawback in breeding.
The purpose of this breeding program was to construct a brown strain that has a yield comparable to the white strains. That is because strains that are used for the production of brown mushrooms have a yield that is, on average, 20-25% lower than strains that produce white mushrooms. The new variety has been trial and field tested and has been found to retain its distinctive characteristics and remain true to type through successive propagations.